Ultra-wideband (UWB) wireless communication technology using the impulse communication scheme does not necessarily require linearity. For this reason, this technology is suitable for making telecommunication equipment based on complementary metal oxide semiconductors (CMOSs), and reducing the size thereof. Additionally, requiring no radio-frequency (RF) circuits, such as highly precise local signal sources, this technology has advantages of lower power consumption and high-speed communication using a broadband.
An impulse waveform generating apparatus for use in UWB wireless telecommunication equipment requires generation of the envelope of an impulse waveform at high precision to control the frequency band to be used. In general, impulse waveform F(t) having band center frequency F0 and bandwidth W in given band frequencies is defined by the [Equation (Eq.)1].
                              F          ⁡                      (            t            )                          =                                            sin              ⁡                              (                                  2                  ⁢                                                                          ⁢                  π                  ⁢                                                                          ⁢                  Wt                                )                                                    π              ⁢                                                          ⁢              t                                ⁢                      cos            ⁡                          (                              2                ⁢                π                ⁢                                                                  ⁢                F                ⁢                                                                  ⁢                0                ⁢                                                                  ⁢                t                            )                                                          [                  Eq          .                                          ⁢          1                ]            
In a known method of generating impulse waveforms, a structure including a digital-to-analog (D/A) converter is used. FIG. 25 is a block diagram of a conventional impulse waveform generating apparatus using a D/A converter. With reference to FIG. 25, conventional impulse waveform generating apparatus 1100 has rectangular-wave oscillator 1111 for generating rectangular waves, storage 1113 for storing voltages corresponding to a waveform table, and D/A converter 1112 for generating an impulse waveform from the supplied rectangular waves according to external voltage.
In conventional impulse waveform generating apparatus 1100, D/A converter 1112 generates a voltage corresponding to the waveform table stored in storage 1113, at the timing of rectangular waves output from rectangular-wave oscillator 1111, and generates impulse waveform F(t) 1114.
This conventional impulse waveform generating apparatus 1100 is capable of generating uniform waveforms at high precision. Additionally, circuit control is easy, and no impulse shaping filter is necessary. Thus, this apparatus is suitable for circuit integration. On the other hand, this apparatus requires sampling rates several times the band frequencies of the impulse waveforms generated in D/A converter 112. For example, generation of an impulse waveform in the band ranging from 3 GHz to 10 GHz inclusive requires a sampling rate of several tens of gigahertz. In general, to structure an impulse waveform generating apparatus using a D/A converter operating at such radio-frequencies, elements having high switching frequencies are used. This structure requires high power consumption.
Japanese Translation of PCT Publication No. 2003-535552 discloses an impulse waveform generating apparatus for generating waveforms approximating the Gaussian primary derived function, using a digital circuit instead of a D/A converter.
FIG. 26 is a block diagram of the conventional impulse waveform generating apparatus using this digital circuit. FIG. 27 is a timing diagram of this conventional impulse waveform generating apparatus.
With reference to FIG. 26, conventional impulse waveform generating apparatus 1300 includes the following elements: clock 1301 for generating clock pulses; buffer 1304; inverting buffer 1306; delay element 1324 having a delay effect, i.e. delay time length “L”; delay element 1308 having a delay effect of “L+X”; AND gate 1316; buffer 1320; inverting buffer 1322; delay element 1310 having delay time length L; delay element 1325 having delay time length L+X; buffers 1332, 1334, 1336, and 1337; adding circuits 1348 and 1350; and switch 1356.
Clock 1301 feeds clock pulses into buffer 1304 and inverting buffer 1306. Buffers 1304 and 1306 feed clock pulses into AND gate 1316 via delay elements 1310 and 1308, respectively. Delay element 1308 has a longer delay effect (X) than delay element 1310. AND gate 1316 outputs AND signal C of supplied signal 1312 (A) and signal 1314 (B). The output from AND gate 1316 is fed into buffer 1320 and inverting buffer 1322 via line 1318, and further passed to delay elements 1324 and 1325 having the same delay effects as delay elements 1310 and 1308, respectively. The output from each of delay elements 1324 and 1325 is divided and fed into buffers 1332, 1334, 1336, and 1337. Then, buffers 1332 and 1334 feed the output without any change into adding circuit 1348 via lines 1340 and 1342, respectively. Buffers 1336 and 1337 feed the inverted output to adding circuit 1350 via lines 1129 and 1346, respectively.
Respective lines 1340, 1342, 1129, and 1346 supply different components that are halves in a positive or negative direction of an individual pulse, such as pulse 1360 shown in FIG. 27. The output from adding circuits 1348 and 1350 are fed into switch 1356 via lines 1352 and 1354, respectively. Control circuit 1358 switches adding circuits 1348 and 1350 so that a bi-phase waveform having prescribed phase “0” is supplied when switch 1356 is at a first setting and the opposite bi-phase waveform is supplied when the switch is in opposite state “1”.
In this manner, in conventional impulse waveform generating apparatus 1300 using a digital circuit, pulse signals are generated from two clock signals having a slight difference in delay effect time length. Then, from the generated pulse signals and inverted pulse signals, pulse signals having a slight difference in delay effect time are generated. Thus, a necessary impulse waveform is generated by the supplied bi-phase waveforms.
Above conventional impulse waveform generating apparatus 1100 using a D/A converter operates at a high operational frequency, and thus has high power consumption.
Above conventional impulse waveform generating apparatus 1300 using a digital circuit generates a waveform only by superimposing impulses. Thus, the waveform cannot be generated at high precision. Further, conventional impulse waveform generating apparatus 1300 has a wide frequency range of generated impulses and requires an impulse shaping filter in the later stage. Thus, the entire circuits cannot be made into integrated circuits.